Comedogenic products clog pores and follicles and inhibit the skin's natural cleansing of sebaceous materials. Sebaceous materials found in the skin are composed of fats, cellular debris and keratin. These sebaceous materials, if trapped within pores or follicles, become a site for the growth of corynebacterium acnes. In a short time these sites also accumulate dirt causing the pore or follicle to become a blackhead or comedone. Such comedones, over time, may become infected and contribute to the onset of acne.
The use of image analysis in conjunction with UV light to evaluate facial comedones is known and is described in Analysis of Facial Comedos by Porphyrin Fluorescence and Image Analysis by G. Sauermann, Ph.D, B. Ebens, Ph.D and U. Hoppe, Ph.D. Porphyrin, which is a class of red pigmented compounds which form the active nucleus of hemoglobin in blood, are synthesized by corynebacterium acnes and are present in the material composing the comedones. The porphyrins fluoresce under ultraviolet light causing the comedones to glow so that they can be either manually counted or analyzed by the use of image analysis software. However, the use of porphyrin fluorescence under UV light has a number of drawbacks: The porphyrin synthesized by the corynebacterium acnes present in the sebaceous glands will fluoresce under UV light only while the bacteria is actively synthesizing porphyrin. Thus, the most reliable UV testing method is to shine the ultraviolet light directly on the subject's skin, in vivo, in order to cause the porphyrins to fluoresce so that the number of comedones on the skin area being analyzed can be more easily seen and counted. However, it is well-known that ultraviolet light emits radiation and overexposure can be hazardous to the skin of the subject as well as to the retinas of the scientist conducting the analysis. Further, using the same UV method upon a removed skin sample is unreliable due to the fact that the corynebacterium acnes only synthesize porphyrins for a very short time in dying skin giving erratic and erroneous comedone counts because porphyrins fluoresce only during synthesis. Another drawback is that not all comedones contain porphyrin which, therefore, would not fluoresce under the UV light resulting in an erroneous comedone count.
Prior to the use of image analysis, follicular biopsy samples were evaluated manually under a stereo microscope. The comedones were counted, sized and each were assigned a number grade global evaluation to the follicular biopsy sample. Global evaluations were based on a standard four-point scale with zero being noncomedogenic and three being comedogenic. However, manual evaluation of follicular biopsy samples is very slow, painstaking and tedious and there may be large differences between evaluation of the same sample depending upon the scientist performing the evaluation.